2-alkoxytetrahydrofurans and their derivatives are useful intermediates in the production of 1,4-diols and other valuable chemicals. See the co-pending application of William Edward Smith, entitled "Butanediols Via Hydrolysis-Hydrogenation of 2-Alkoxytetrahydrofurans" filed on even date herewith under Ser. No. 806,074, now U.S. Pat. No. 4,091,041 assigned to the same assignee as the instant application, and incorporated by reference herein.
There have been several reports describing the synthesis of 2-alkoxytetrahydrofuran derivatives. By way of illustration, Lawesson and Berglund, Acta. Chem. Scand. 14, 1854-5 (1960), generated a number of the subject compounds by decomposing t-butyl perbenzoate in the presence of alkanol-tetrahydrofuran mixtures. Furthermore, Kratochvil and Hort Czech. 103, 203 (1962), produced 2-methoxytetrahydrofuran by the low temperature photochlorination of tetrahydrofuran in the presence of methanol and an HCl acceptor.
It has also long been known that allyl alcohol can serve as a substrate for the hydroformylation reaction, affording hydroxyaldehyde products. Adkins and Kresek, Journal of the American Chemical Society, 70, 383 (1948) and 71, 3051 (1949) reported the synthesis of 4-hydroxybutyraldehyde in 30% yield by the cobalt carbonyl-catalyzed hydroformylation of allyl alcohol. Brown and Wilkinson, Tetrahedron Letters 1969, (22), 1725-6 and Journal of the Chemical Society (A), 1970, 2753-64, reported the hydroformylation of allyl alcohol and a number of other olefins in the presence of hydridocarbonyltris-(triphenylphosphine) rhodium (I) as catalyst, which produced the corresponding aldehydes. Pruett and Smith in U.S. Pat. No. 3,917,661 claim a process for producing oxo aldehydes from olefins using a rhodium carbonyl catalyst system modified by triorgano phosphorus ligands of the group consisting of trialkylphosphites, tricycloalkylphosphites, triarylphosphites, and triarylphosphines.
In German Pat. No. 2,538,364, Schimizu describes a process by which allyl alcohol is converted to an aldehyde mixture by hydroformylation in the presence of a rhodium carbonyl catalyst modified by any of a number of triorgano phosphorus ligands, and the aldehydes are separated by aqueous extraction and converted to butanediol in a separate, conventional hydrogenation procedure.
U.S. Pat. No. 3,239,566 of Slaugh et al discloses the use of phosphine-rhodium carbonyl complex catalysts in oxo reactions producing aldehydes and/or alcohols at temperatures exemplified at 195.degree. C.
As a result of investigating the hydroformylation of allyl alcohol under the influence of a triphenylarsine-modified rhodium carbonyl catalyst, a minor product not encountered in previous studies with other catalyst systems, has now been isolated and identified as 2-n-propoxytetrahydrofuran. It appears that this compound is formed in a secondary reaction involving hydroformylation and hydrogenation derivatives of allyl alcohol. This point was then verified and a synthetically useful process has now been discovered, and is the subject of this invention. In essence, the hydroformylation according to this invention is to be carried out in the presence of a co-reactant quantity of an alkanol by the following pathway: ##STR1## wherein R is hydrogen or alkyl and R.sup.1 is alkyl or hydroxyalkyl.
In all cases, the corresponding 2-alkoxytetrahydrofuran is formed in good yield.